LAMELLIBRANCHIATA. 509 



nearly straight, abruptly recurving at the posterior extremity, which is 

 almost vertically truncate. Cardinal line straight, scarcely declining poste- 

 riorly. Anterior end short and abruptly rounded below. 



Valves regularly convex below, becoming gibbous in the middle and above. 



Beaks near the anterior third, incurved and rising but. little above the 

 hinge-line. Umbonal slope obtusely angular, extending to the post-inferior 

 extremity. 



Surface marked by fine concentric striae, which become fasciculate and are 

 elevated into somewhat irregular concentric undulations, which extend from 

 near the anterior end over the umbonal slope. Interior unknown. 



Two specimens measure respectively 24 and 22 mm. in length, and 13 and 

 Vi mm. in height. 



Formation and localities. In the arenaceous shales of the Chemung group, at 

 Counewango, Cattiiraugus county, and Cherry Creek, Chautauqua county, N. Y. 



PROTOMYA, N. G. 

 Protomya oblonga. 



PLATK LXUI, FIG. 21. 

 Cardiomorpha oblonga. Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 63, lig-. 21. 1883. 



Shell large, elongate-ovate, narrower behind ; length twice the height ; basal 

 margin very gently curving. Posterior extremity gaping, regularly rounded. 

 Cardinal line gently declining posteriorly. Anterior end large, rounded. 



Valves moderately and regularly convex. 



Beaks a little anterior to the middle of the length, low, not strongly de- 

 fined, rising but little above the hinge-line. Umbonal slope regularly con- 

 vex, not defined. 



Surface, in the cast, marked by fine concentric striae, which are aggregated 

 into fascicles, producing low undulations of the surface. 



Anterior muscular impression strongly marked, situated just within the 

 65 



